Erosion of pipe walls has long plagued the chemical and oil and gas industries. In the chemical industries this erosion is usually due to the corrosive nature of the gas or liquids being carried in the pipes. In the oil and gas industry the erosion is most commonly mechanical in nature being caused by the impacting of solid materials carried by the flowing oil and gas as it passes through the pipes. These materials are most commonly sand which is brought to the surface by the hydrocarbons from the oil or gas reservoir which is being tapped. Pressures within the piping, whether the piping is being used in the chemical industry or in the oil and gas industry are often quite high. In the chemical industry such high pressures are the result of process pressures which are needed to accomplish the process being utilized. In the oil and gas industries the pressures are the result of the production from high pressure oil and gas reservoirs.
It can be appreciated that monitoring the amount of erosion taking place within the pipe is essential from both a safety aspect and a financial aspect. Should the erosion continue unmonitored there will be a point at which the piping wall becomes so thin that rupture of the piping will occur. Should any personnel be in the vicinity physical harm to these people is almost eminent. Also, from the financial aspect, rupture of piping can be catastrophic to adjacent equipment, not to mention the costly interruption of the chemical process or the gas and oil production being practiced at the time of failure. So well recognized is the necessity for monitoring the effects of erosion, several procedures have been developed which are nearly ubiquitous.
Two of the most widely utilized procedures provide intermittent monitoring. Generally a schedule is set up which invokes periodic checks, the length between checks being dependent upon the anticipated erosion rate. These two procedures are generally classified as radiographic inspection and ultrasonic inspection. The biggest drawback in utilizing these two procedures is their intermittent nature and do not provide continuous monitoring as would be the case in a passive monitoring system. This disadvantage is easily understood when it is considered, for example in the oil and gas industry, that the rate of erosion is not always constant. In producing oil and gas a producer attempts to achieve production without pulling sand from the reservoir along with the oil or gas product. However, this pulling of sand from the reservoir is not always preventable due to the uncertain nature of conditions found in the reservoir. Thus large amounts of sand may be flowing with the oil or gas product on an intermittent basis without the knowledge of the producer. As mentioned previously, this sand will cause erosion and since it can very well be on an intermittent basis the rate of erosion is not at all predictable. In the chemical industry intermittent erosion rates beyond that which is anticipated can also occur due to unit upset. Thus, when the inspection of the pipe walls is placed on a periodic basis there is always the possibility that erosion has occurred much faster than anticipated and that the inspections will not have the frequency required to warn of impending piping failure.
Not only is the very nature of radiographic and ultrasonic inspection, due to its periodic use, disadvantageous but the very procedures themselves are not without difficulty. In radiographic inspection, radioactive materials such as Iridium 192 or Cobalt 60 are utilized which always presents a hazard to the inspector and to any personnel around the inspection site. Also radiographic inspection is very time-consuming and as a result thereof is very costly. While ultrasonic inspection does not entail the use of radioactive material, it also has some drawbacks. For one, the surface of the pipe on which the inspection test is to be run must be prepared so that it is clean from rust, paint and other extraneous materials. If the rust buildup is quite heavy it will be necessary for the inspector to file the rust from the pipe which could be extremely dangerous if the pipe is near its bursting point. Also there will be a situation in which cleaning of the pipe may be nearly impossible due to the fact that the pipe is in an environment which makes cleaning an almost impossible task. For example, in off-shorer oil and gas operations the pipe to be tested may be located near the water line so that the wave action is continuously washing over the pipe making cleansing of the pipe for the purpose of ultrasonic inspection impossible. Ultrasonic inspectionn also suffers from the requirement that the device needs to be calibrated and such calibration is a time-consuming procedure.
Therefore there is a need for a system which will continuously monitor the wall thickness of pipe and will automatically notify the process operator or producer that the pipe wall has become dangerously thin. It is also desirable that such a system not require the use of hazardous, radioactive material or require time-consuming surface preparation or calibration.